Electronic states and optical properties of Si/SiO2 superlattices

We study the electronic structure of {Si}(m){SiO2}(n) superlattices (SLs) g rown along the [001] direction, using tight-binding methods. Detailed atomi c models of the Si/SiO2 interface are considered. A clear feature of the re sults is the essentially direct band-gap structure with flat bands along th e Z Gamma symmetry line of the SL-Brillouin zone which has a blueshifted en ergy gap due to quantum confinement. The calculated densities of states are enhanced at the valence and conduction band edges, as compared with silico n. The optical properties of the SLs are calculated using a parametrization of the imaginary part of the dielectric function of bulk Si. The strong co nfinement of the electron-hole pairs in the Si wells and their tendency to localize at the low-dielectric {SiO2} interfaces due to the mutual Coulomb attraction lead to strong electrostatic effects. These produce an interplay of several length scales in determining possible regimes of high radiative efficiency. Our results have implications for the understanding of the lum inescence in porous Si and Si-based nanostructures like the amorphous Si/Si O2 SLs studied recently. (C) 1999 American Institute of Physics. [S0021-897 9(99)07613-6].